I am researching this issue and am experiencing a very similar if not identical issue.

I have been on Quickbooks 2012 (2012 not 2021) Desktop for a decade.  I use manual payroll since I have only 1 employee, my spouse, and the data has not changed in 20 years for the monthly salary.  In QB2012 I would enter checks and could use QB2012 to export tax forms to Excel to generate the QB designed reports for the 941, 940, W2 and W3.  My CPA handles it from there and set things up so that is all he wants/needs.

Late last year I decided to try upgrading from QB2012 to QB2021 DESKTOP (without the subscription and without the added payroll service).   I made a copy of the QB2012 data file for testing in QB2021 (I have stuck with QB2012 until a migration is fully tested and operational).   QB2021 opened the QB2012 datafile and updated it to the QB2021 company file format (whatever that means).  When it happened, the Excel reports for Vendors (1099s for example) stopped working as did the Excel reports for employees.  On the 1099s I finally reset enough vendor settings or category settings to get the 1099 reports to work again - this seemed to relate to some things needing to generate as 1099-MISC and others to generate as 1099-NEC which previously were all on 1099-MISC.   However, the employee reports still are not working after at least a week of uninstalling, reinstalling, running QB Hub, editing employee records, adding "dummy" employee records, etc., - it just is not working.

in QB 2021, I can generate a payroll check just I have been doing in QB2012. I was also able to load and generate the entries to process payroll liabilities.  I can generate employee reports WITHIN QB2021 regarding various employee issues. However, what I am trying to do is to use the menu option to export employee reports into Excel. When I try to run the report to create payroll forms in Excel, Excel loads, a QB template of some form loads and it allows me to select which report I want to generate (941, 940, W2, W3, etc.). I can pick any one of the reports and it generates within Excel but all of the fields (name of employee, dollar amounts, address, etc.) are all empty or zero.

So, it appears it should be working just as it did in QB2012 but for some reason I have not located, its not sending the available data fields to Excel.

Another odd event I noticed. If I go to "Employee Center" in QB2021 there is a submenu that has add new employee, etc., and one option is EXCEL. Under the EXCEL option is "Summarize Payroll Data in Excel". I can run that report - HOWEVER - it generates an Excel report for 3 employees that have never worked for me, they are not listed in employee center, and all the record entries are in 2007. Then there is another report under the EXCEL Tab that says "summarize transactions". If I run it, it generates a report of the 2021 payroll check "net" amounts for my single employee that is ACCURATE.

So, again it seems that QB2021 is trying to generate the payroll tax forms but it is not sending data that QB2012 did.